Phase composition and morphology characteristics of ceria-stabilized zirconia powders obtained via sol-gel method with various pH conditions.

PURPOSE: High purity, fine crystalline, degradation-free at low temperature powders have attracted special interest in CAD/CAM prosthetic dentistry full ceramic restorations. This study reports the preparation and characterisation of zirconia-ceria (0.9 ZrO2 0.1 CeO2) powders. Materials were obtained from zirconium-n-alkoxide and cerium nitrate hexahydrate in the pH 2-4 and 8-10. METHODS: Zirconia- ceria powders were obtained with the sol-gel method in a humid-free environment. Thermal analysis (TGA/DTA) of the as-prepared materials was made for an assessment of its behaviour at elevated temperatures. Specimens were dried at 80 °C and calcinated in two stages: at 300 °C with soaking time 2.5 h and 850 °C with holding time 2.5 h, in order to evaluate the phase transformations. Thermal analyses of the as-dried powders were made for an assessment of its thermal behaviour during heat treatment up to 1000 °C. By X-ray diffraction (XRD), polymorphs of ZrO2 were identified. Additionally, scanning electron microscopy (SEM) and laser particle size distribution (PSD) were involved for characterisation of morphology of the powders. RESULTS: A correlation between the pH of the colloidal system and the morphology of the as-obtained powders were found. Based on analysis (SEM, PSD), structures were identified known as soft and hard agglomerates. CONCLUSIONS: It can be stated that differences found between powder morphology were dependent on the value pH used, which can be crucial for powder densification during sintering and compacting green bodies which, as a consequence, may be crucial for the lifetime of zirconia prostheses. Correlations between phase composition and pH are difficult to grasp, and require further, more sophisticated, studies.

A Simple Densimetric Method to Determine Saturation Temperature of Aqueous Potassium Chloride Solution.

The precise control of crystallization is a key issue in providing a high quality crystalline product. It has to be achieved by, among other means, a proper choice of the solution processing temperature, which is determined on the basis of the metastable zone width and type of solubility curve. In this article experimental data for potassium chloride solution density, as a function of temperature and its correlation in the range from under- to supersaturation, are reported for solution concentrations between 24.62 % w/w and 31.84 % w/w. As could be expected in the case of undersaturated solutions and low supersaturation, the temperature dependence of density for solutions of different saturation may be described by a linear equation within the investigated range of concentrations. It was also proved that for the undersaturation range there exists a pole point, which allows calculation of the saturation temperature, based on the density measured at any temperature.